function S = area_cal2(alpha,theta)
alpha1 = alpha*pi/180;
alpha2 = pi - alpha*pi/180;
theta = theta*pi/180;
d = 2*10*cos(alpha1);
px = tan(alpha2-theta).*d./(tan(alpha2-theta)-tan(alpha1+theta));
py = tan(alpha1+theta).*tan(alpha2-theta).*d./(tan(alpha2-theta)-tan(alpha1+theta));
mx = tan(alpha2+theta).*d./(tan(alpha2+theta)-tan(alpha1+theta));
my = tan(alpha1+theta).*tan(alpha2+theta).*d./(tan(alpha2+theta)-tan(alpha1+theta));
nx = tan(alpha2+theta).*d./(tan(alpha2+theta)-tan(alpha1-theta));
ny = tan(alpha1-theta).*tan(alpha2+theta).*d./(tan(alpha2+theta)-tan(alpha1-theta));
ox = tan(alpha2-theta).*d./(tan(alpha2-theta)-tan(alpha1-theta));
oy = tan(alpha1-theta).*tan(alpha2-theta).*d./(tan(alpha2-theta)-tan(alpha1-theta));
Lpm = sqrt((px-mx).^2+(py-my).^2);
Lmn = sqrt((mx-nx).^2+(my-ny).^2);
Lno = sqrt((nx-ox).^2+(ny-oy).^2);
Lpn = sqrt((px-nx).^2+(py-ny).^2);
Lop = sqrt((ox-px).^2+(oy-py).^2);
S = sqrt((Lpm+Lmn+Lpn).*(Lmn+Lpn-Lpm).*(Lpm+Lpn-Lmn).*(Lpm+Lmn-Lpn)/16)+...
sqrt((Lpn+Lno+Lop).*(Lno+Lop-Lpn).*(Lpn-Lno+Lop).*(Lpn+Lno-Lop)/16);
end

